Hydraulically powered shear



Sept. 18, 1962 J. B. CASTLE, JR 3,054,317

HYDRAULICALLY POWERED SHEAR Original Filed June 25, 1954 8 Sheets-Sheet1 INV EN TOR z/PIMES 5. C snzzi BY M M ATTORNEY 5 Sept. 18, 1962 J. B.CASTLE, JR

HYDRAULICALLY POWERED SHEAR 8 Sheets-Sheet 2 Original Filed June 25,1954 INV EN TOR J /wss 5. Giana/Z ATTORNEY .5

Sept. 18, 1962 J. B. CASTLE, JR

HYDRAULICALLY POWERED SHEAR 8 Sheets-Sheet 3 Original Filed June 25,1954 r/A'MES 5. Oasnszlh BY M M ATTORNEYS Sept. 18, 1962 J. B. CASTLE,JR

HYDRAULICALLY POWERED SHEAR Original Filed June 25, 1954 8 Sheets-Sheet4 K 3 T n N 5 m 5 5 m J u m ATTORNEYS Sept. 18, 1962 J. B. CASTLE, JR

HYDRAULICALLY POWERED SHEAR Original Filed June 25, 1954 8 Sheets-Sheet5 R m m M z/ZMES 5. C srLErZz- ATTORNEYS Sept. 18, 1962 J. B. CASTLE, JR3,054,317

HYDRAULICALLY POWERED SHEAR Original Filed June 25, 1954 8 Sheets$heet 6CH- ll L (n C A w N 5 O a j IN VENTOR BY myflwzw ATTORNEYS Sept. 18,1962 J; B. CASTLE, JR

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M @wvz/ ATTORNEYS Sept. 18, 1962 J. B. CASTLE, JR 3,054,317

HYDRAULICALLY POWERED SHEAR Original Filed June 25, 1954 8 Sheets-Sheet8 N i g 1 I g 1 i m i l i Q I INVENTOR N JAMES 5. 645mm]? n I n \l I) QBY M 9 M ATTORNEYS United States Patent 1 Claim. (Cl. 83-399) Thepresent invention relates in general to hydraulically powered machineswith movable rams and more particularly to a shear in which the ramconstitutes a shearing blade.

This application is a division of my application for HydraulicallyPowered Machine, Serial No. 439,349, filed June 25, 1954.

Among the objects of my invention are:

(1) To provide a novel and improved power shear.

(2) To provide a novel and improved power shear of the hydraulic type inwhich the established rake angle of the movable knife or blade is resetduring each cycle of operation to avoid the effects of an accumulationof departures from the established angle.

Additional objects of the invention will be brought out in the followingdescription of a preferred embodiment of the same as applied to a shear,taken in conjunction with the accompanying drawings, wherein,

FIGURE 1 is a front view in elevation of a hydraulically powered shearincorporating the present invention;

FIGURE 2 is a left side view in elevation of the shear of FIGURE 1, withan included drive cylinder assembly in section;

FIGURE 3 is a similar view in elevation, of the right side of themachine of FIGURE 1;

FIGURE 4 is a rear View of the shear of FIGURE 1;

FIGURE 5 is a plan view of the shear of FIGURE 1 looking down fromabove;

FIGURE 6 is a schematic view of a hydraulic system for powering theshear blade of the machine of FIGURE 1;

FIGURE 7 is a schematic view of a hydraulic system for operatingassociated components of the machine of FIGURE 1;

FIGURE 8 is a wiring diagram depicting the electric circuits involved incontrolling the operation of the operation of the machine of FIGURE 1;and

FIGURE 9 is a view partly in section of a hold down device embodied inthe machine of FIGURE 1.

Referring to the drawings for details of the invention in the form of ahydraulically powered shear, the same comprises a frame 1 involving apair of spaced side walls 3 and 5, each formed with a relatively deepthroat 7 in the front edge thereof. Joining the side walls along thefront edges below the throats, is a front wall 9, while extendingoutwardly from the front wall along its upper edge is a work table 11,the front wall and table being formed into a rugged unit by integralbrackets 13 extending from the front wall in supporting relationship tothe table.

The front wall and table unit is recessed at the junction of the tableand front Wall to receive a stationary blade 15 forming a component ofthe shearing mechamsm.

The front edge portions of the side walls above the throats are set backsomewhat to permit of supporting the ram or movable blade 17 of theshearing mechanism Patented Sept. 18, 1962 in proper relationship to thefixed component. Such movable blade includes a main body portion 19 anda shearing component 21 affixed thereto at an angle to the horizontal,along the lower edge thereof, and is strengthened by a horizontalbracing rib 23 of substantial depth.

For the purpose of mounting the blade, a pair of ways 25, 27 are afiixedto the upper front edges of the side walls, such ways being tilted at avery slight forward angle of the order of 2 degrees, preferably byforming the edges of the side walls at such an angle, and the blade isslidably mounted on the ways by guide channels 29, 31 affixed to therear side of the blade and in engagement with the ways.

The operating movements of the blade are controlled hydraulically by asystem including a left cylinder assembly 33 and a right cylinderassembly 35, fixed to the upper front edges of the side walls of thehousing and coupled to the blade. Thus each end of the blade will bepowered by one of these cylinder assemblies.

Each cylinder assembly involves a closed dome shaped cylinder 37 whichis affixed to the upper front edge of the associated side wall andincludes therein a recessed piston 39 extending through the lower end ofthe cylinder for connection to the upper edge of the blade.

Hydraulic pressure is derived from a pump 43 operated by an electricmotor 45, the pump having its suction end connected to a reservoir orsupply tank 47 and its discharge end connected through a flow line 49 toa threeposition main operating valve 51. This main operating valvenormally occupies a neutral position as illustrated in the drawings, inwhich position the pump is connected directly back to the tank, thusby-passing the rest of the system. The valve is capable of being shiftedin either of opposite directions to occupy either one position whichdetermines the work stroke of the blade, or another position whichdetermines the return stroke of the blade. The direction of shift isdetermined by selective energization of one of a pair of solenoids 53and 55 associated with the valve, that solenoid 53 which determines thework stroke of the blade being designated the down solenoid, while theother solenoid 55 which determines the return stroke of the blade, isdesignated the up solenoid.

In lieu of utilizing a conventional tank for holding the supply ofliquid, it is noted that the tank 47 is in the form of a section of pipeof substantial diameter con nected between the side walls of the frameand thus constituting a structural member of the frame.

From the main operating valve, a flow line 57 extends to and enters theleft cylinder at a point above the piston. From a point in that cylinderbelow the piston, a connecting line 59 couples this cylinder to theright cylinder at a point above the piston enclosed therein, while froma point in the right cylinder below the piston, a line 61 leads back tothe main operating valve.

Included in this latter line, is a counter-balance valve 63. Thecounter-balance valve employed at this point, is a conventional typevalve having a normally closed passage 65 therethrough, but which isadapted to be shifted to a connecting position against a spring load 67by pressure of liquid applied through a branch passage 69 to overcomethe action of the loading spring. Thus, in order for liquid to flowthrough such valve, the pressure of liquid in the system in thedirection of the flow through the valve must first build up to a valuesufiicient to overcome the spring load. Such spring loading may be fixedat any desired value, determined by the operating requirements of thesystem.

The counter-balance valve referred to is by-passed in the direction ofreverse flow, by a check valve 71 which permits free flow of liquidaround the valve with essentially no pressure drop at this point in thesystem.

It will be apparent that the system as thus far described, provides fora series connection of the cylinder assemblies, and that the workperformed by the piston in the left cylinder will be apportioned betweenthat imparted to the blade at that end and the work performed by thepiston in the right cylinder, as conveyed to such piston through theconnecting line between the two cylinders.

With the down solenoid energized, the main operating valve will beshifted to the left, as viewed in the drawing, whereby the pump will beconnected to the left cylinder and the return line from the rightcylinder will be connected back to the tank from which the pump drawsits supply of liquid. Under these conditions, the blade will be forceddownward under relatively low pressure determined by the spring loadingon the counter-balance valve, until the blade engages the work, when thepressure in the system will necessarily rise to a value sufiicient toperform the shearing operation.

With the up solenoid of the main operating valve energized, this valvewill be shifted to its extreme right position as viewed in the drawing,whereupon, the pump will be connected to the lower end of the rightcylinder through the check valve, while the line from the left cylinderwill be connected to the tank. The resulting reverse flow of liquid inthe system will serve to raise the blade to its up position. At its upposition, it will be retained due to the spring loading of thecounter-balance valve which is made more than adequate to resistdropping of the blade under its own weight.

As a protection against pressures substantially beyond safe operatingvalues, a spring loaded relief valve 73 is connected between thedischarge side of the pump and its source of supply, the tank 47.

An important feature of the basic system, as thus far described, residesin the means provided for assuring equal rate of travel of both ends ofthe blade at all times. This is accomplished in the most simple manner,which becomes an inherent part of the operation of the system, by soconstructing the cylinder assemblies that the under side 75 of the leftpiston equals in area, within manufacturing tolerances, the area of theupper surface 77 of the right piston. When so dimensioned, all otherfactors remaining constant, both pistons will inherently move at thesame rate.

A study and analysis of the series hydraulic drive system described,shows that total power applied to the blade, while it remains constantunder constant load conditions, varies in respect to the ratio ofapportionment between the ends of the blade in accordance with theprogressively shifting load as shearing takes place. Such apportionmentof applied power, furthermore, is such as to maintain equilibrium ofmoments about the continually shifting point of contact between theblade and the work during shearing.

Operations of the blade are initiated by an operator through theexpediency of a foot controlled switch 79 forming a component of anelectrical system, which not only includes the various solenoidsassociated with the many valves of the basic hydraulic system previouslydescribed, but also an upper limit switch 81 and a lower limit switch 83mounted on the machine, for determining the beginning of the stroke ofthe blade and the termination thereof.

The upper limit switch is a single contact switch of the normally closedtype involving a spring armature 85 in engagement with a contact 87while the lower limit switch is of the double acting type having aspring armature 89 normally in contact with an upper contact 91 Whileout of engagement with a second contact 93. Both limit switches arecarried by a bracket 95 affixed to a side wall of the machine, with theswitches in position to be engaged by an upper limit stop 97 and a lowerlimit stop 99 mounted on the blade.

The upper limit stop may take the form of an adjustable screw 101threaded in the end of an L-shaped bracket 103, while the lower limitstop may take the form of a cylinder 105, closed at one end and disposedover the upper end of the L-shaped bracket. This cylinder has its loweredge 167 cammed for engagement with the lower limit switch at a selectedpoint on the cammed edge determined by rotational adjustment of thecylinder, to effect a change in stroke of the blade, which in turn canbe relied on to effect a change in the length of cut of the blade, itbeing recalled, that the lower edge of the blade is angularly disposedwith respect to the horizontal.

Any suitable means may be relied upon for holding such an adjustment,and as one example, the upper end of the L-shaped bracket might bereduced and passed through the upper or closed end of the cylinder toreceive a nut 109, with a compression spring 111 disposed between thenut and the adjusting cylinder. By forming the cammed cylinder with aflange 113 at its upper end, a hand grip is provided to facilitate themaking of adjustments.

The foot controlled switch is of the normal open type and involves afoot operated armature 115 adapted, upon foot actuation thereof, to makeconnection with a contact 117 which is connected to one side of a powersupply 119. The armature in turn is connected to the armature of thelower limit switch, which in the upper position of the shear blade,contacts the upper contact of such switch. This contact is in turnconnected to the other side of the power supply through a pair ofnormally bridged contacts 121 of an up relay 122 and a pair of seriesconnected windings 123, 125 of a timing relay 127. One of such windings123, controls a pair of associated normally open contacts 129 which, inresponse to energization of the winding 123, close a circuit through thewinding 131 of a down relay 132.

This down relay controls a pair of normally bridged contacts 133 and twopairs of normally open contacts 135 and 137 respectively. Whenenergized, one of the pairs 135, of normally open contacts, closes acircuit from the power supply through the down solenoid 53 associatedwith the main operating valve, to shift the main operating valve to aposition for producing a down or work stroke of the shear blade.

Immediately upon initiation of the down stroke of the blade, the upperlimit stop is withdrawn from engagement with the upper limit switch,thus permitting this upper limit switch to close. The contact of thisswitch is connected to the blade 141 of a single pole switch 143 whosecontact 145 is connected through the winding 147 of the up relay, to oneside of the power supply, while the armature of the upper limit switchis connected through the pair of normally bridged contacts 133 of thedown relay to the other side of the power supply.

However, since at this moment the down relay is energized and itsnormally bridged contacts are open, nothing happens upon such closing ofthe upper limit switch, even were the single blade switch closed.

As the shear blade reaches the lower limit of its stroke, as determinedby the setting of the cammed cylinder, contact with the upper contact ofthe upper limit switch is broken, while at the same instant, engagementof the armature with the lower contact is effected.

Opening of the circuit at the upper contact serves to de-energize thetiming relay 127, whereupon the circuit through the winding of the downrelay is opened and the contacts thereof restored to normalcy. Theopening of the contacts in the circuit of the down solenoid, deenergizesthe down solenoid and permits the main operating valve to restore itselfto its neutral position and thereby halt the downward movement of theshear blade.

Restoration of the contacts of the down relay to normalcy, will furthercomplete a circuit by way of its normally closed contacts 133 throughthe upper limit switch and the wniding of the up relay, if the singlepole switch 143 in circuit with the winding of such relay is in itsclosed position. Under such condition, the up relay will then becomeenergized, and through the resulting bridging of a pair of normally opencontacts 149, will establish a circuit to the up solenoid of the mainoperating valve and cause such valve to shift to that position whichdetermines upward movement of the blade, to thereby initiate a returnstroke of the blade.

Such upward movement of the blade will continue until the upper limitstop engages the upper limit switch and opens the same, therebyde-energizing the up relay, which in turn will open the circuit to theup solenoid and cause the main operating valve to establish itself againin its neutral position, whereby the blade will come to a halt at theupper limit of its return stroke.

During the downward or work stroke of the blade, the travel of the bladeis under control of the foot control switch, whereby upon removal offoot pressure at any point in the work stroke, the blade may be broughtto a complete halt, or moved downwardly at increments at the will of theoperator, until the lower limit of travel is reached, as determined byopening of the lower limit switch. At this moment, if the single poleswitch is in closed position, the up solenoid will become energized andtake over, and start the blade on its return stroke.

With such single pole switch in its open position, the blade will cometo a dead stop at the lower limit of its work stroke.

Should the nature of the work to be performed, make it desirable topermit uninterrupted movement of the blade during its down stroke andthereby relieve the operator of the necessity of maintaining footpressure on the foot control switch throughout such stroke beyond thepoint of initiating such stroke, this objective can be accomplished byshunting the switch following initiation of the work stroke of theblade. A shunting circuit across the foot control switch, including asingle pole switch 151 and the pair of normally open contacts 137 of thedown relay will, when the single pole switch is closed, serve thispurpose, for it will become apparent that upon energization of the downrelay, the shunting circuit will be completed, thus rendering the footcontrol switch ineffective throughout the remainder of the work stroke.

Referring back to the hydraulic system of FIGURE 6, there is includedtherein, means for leveling off the blade in the event the blade, forsome reason or other, assumes a slight tilt. Toward this end, the rightcylinder assembly 35 is shunted by a normally closed valve 155 in serieswith a check valve 157 permitting flow of liquid only in the directionexisting during an up stroke of the shear blade. The valve 155 iselectrically actuable through an associated solenoid 156.

A second normally closed valve 159 is connected between the upper end ofthe right cylinder assembly and the supply source or tank 47 and likethe valve 155, is electrically actuable through a solenoid 161.

Upon energization of the solenoid of the first valve 155, which opensthe valve, the liquid flow will by-pass the right cylinder assembly 35and flow through the connecting line 59 to the underside of the pistonin the left cylinder assembly 33, to thereby exert a lifting forceagainst this piston to the exclusion of the piston in the right cylinderassembly. Thus the opening of this valve 155 will function to compensatefor a situation where the piston in the left cylinder assembly lags thatin the other.

On the other hand, nergization of the solenoid of the second valve 159which effects a connection to the tank from the upper end of the rightcylinder assembly, will establish an effective by-pass around the leftcylinder assembly 33 and thereby produce a lifting force on the pistonof the right cylinder assembly to the exclusion of the piston in theother assembly, to correct a situation where the right piston lags theleft piston.

In causing these leveling valves to respond to tilting of the blade, thesolenoid 156 of the valve is connected across the electrical powersupply through a normally open micro-switch 165, while the solenoid 161of valve 159 is similarly connected through a normally open micro-switch167, with each switch involving a contact 169 in normal open relation toan actuable armature 171 and both switches being disposed in opposingrelationship to each other in a housing 173 afiixed to a side wall ofthe machine.

A bar 175 pivotally mounted at an intermediate point thereof, in saidhousing with its upper end lying between the actuable armatures of thelevel control micro-switches, is adapted to close one or the other ofthe switches when swung in one direction or the other on its pivot axis.

To convert the tilt of the blad to appropriate swing of the pivot bar, alever 177 extending from the pivot bar has its free end coupled to oneend of a cable 179 which runs downwardly under a pulley 181 mounted onthe back of the blade just below the lever, such cable then extendingacross the back of the blade and over another pulley 183 mounted on theback of the blade at the opposite end thereof. The cable is thenanchored to a bracket 185 mounted on the side Wall of the machineadjacent that end of the blade. Tension on the cable is maintained by aspring 187 holding the lever arm in a position which will maintain thepivot bar out of contact with the microswitches when the blade is in alevel position.

It will be apparent, therefore, that should the blade tilt in onedirection or the other, the pivot bar will be actuated accordingly, toclose one or the other of the microswitches and thereby actuate theproper leveling Valve to restore the blade to its level condition.

Inasmuch as leveling is corrected only on the up stroke of the blade,the electrical circuits for the leveling valves, by way of a common line189, are run through a normally open pair of contacts 191 on the uprelay, whereby operation of the leveling valves can occur only followingenergization of the up relay.

In connection with the movements of the shear blade, it is quiteessential that the work upon which the blade is to perform its shearingfunction, shall be immobilized during a shearing operation to ensureaccuracy in the results sought. A feature of the present machine is theprovision of a plurality of hold down devices 193 which are, inaccordance with the present invention, mounted on the movable shearblade for movement therewith.

Each of these hold down devices involves a cylinder 195, a piston 197slidable therein, and a cylinder head 199 closing the upper end of thecylinder and having means in the form of a pipe fitting 201 for theintroduction of liquid into the cylinder under pressure, for actuationof the piston.

The piston may be slidably sealed to the inner wall of the cylinder by aconventional cup leather seal 203, and is formed with an intregal holddown rod 295 extending through the lower end of the cylinder where it isslidably sealed thereto by O-rings 207 resting in grooves formed on theinner wall of the cylinder adjacent the lower end thereof.

At a location intermediate the piston and the O-ring seals, the cylinderis provided with an inner wall groove 209 to trap any oil which may leakpast the piston, thereafter to be withdrawn from the cylinder through asuitable fitting 211 passing through the wall of the cylinder at thatpoint, thus to preclude possible leakage past the O-rings and on to thework. The groove and fitting at the same time serve to vent the cylinderand thereby permit reciprocation of the piston therein.

Each of the aforementioned hold down devices is connected at its upperend by a pipe connection 213 to 7 a manifold 215 which in turn isconnected through a flow line 217 to an accumulator or pressure tank 219wherein a supply 221 of oil is maintained under pressure of an aircushion 223, the tank having a valve fitting 225 for air charging thetank when necessary to provide the proper conditions therein.

In the flow line to the pressure tank, is a hold down control valveassembly 227 involving a pair of normally closed counter-balance valves229, 231 reversely disposed in parallel branch connections whereby flowin either direction in the fiow line 217 may be realized, depending uponwhich of the counter-balance valves is actuated from its normally closedcondition to an open condition.

As previously explained, a counter-balance valve is a conventional typevalve having a normally closed passage 65 therethrough, which is adaptedto be shifted to a connecting position against a spring load 67 bypressure of liquid applied through a branch passage 69 to overcome theaction of the loading spring.

In connection with that counter-balance valve 231, which permits flow tothe hold down devices, a normally closed hold down pilot valve 235,electrically actuable through energization of an associated solenoid237, is coupled into the branch passage of this valve, in series with acheck valve 239 permitting flow in this branch passage only in thedirection of opening of the counterbalance valve with which it isassociated.

The solenoid 237 of the hold down pilot valve is electricallyconnectible in a circuit across the power supply through the normallyopen contacts 241 associated with the second winding 125 of the timingrelay 127 and the normally closed pair of contacts 133 of the downrelay. Insofar as this circuit is concerned, it will be apparent thatthe hold down pilot valve will become energized immediately uponenergization of the timing relay 127, which occurs in response toclosing of the foot operated switch with the shear blade at its upposition.

In response to such energization of the hold down pilot valve, a freeflow of liquid under pressure of the air cushion in the pressure tank,will be permitted to the upper ends of the cylinders of the hold downdevices whereby the piston in each of such devices will be urged towardthe work from a normally extended position.

By associating a dash pot 245 with the normally open contacts of thefirst winding 123 of the timing relay, a time delay may be introduced inthe energization of the down relay, sufficient to permit the pistons ofthe hold down devices to move down and engage the work, before the downrelay is energized and opens the circuit to the hold down pilot valve.Thus by the introduction of such time delay, the hold down pistons willbe in engagement with the work prior to the movement of the shear bladetoward the work.

With downward movement of the shear blade, the hold down cylinders willbe forced down over their pistons thus driving oil out of the cylindersand back into the pressure tank, but through the other counter-balancevalve 229. By adjustment of the spring loading of this valve, adequatehold down pressure by the hold down pistons, will be automaticallyrealized in response to such downward movement of the shear blade.

Referring again to the electrical circuit diagram in the drawings, itwill be noted that the solenoid 237 of the hold down pilot valve is alsoconnectible across the power supply through the normally closed pair ofcontacts 133 of the down relay and a normally open pair of contacts 247of the up relay, whereby when the down relay is de-energized and the uprelay is energized, the hold down pilot valve solenoid will be connectedin circuit across the power supply.

Inasmuch as the de-energizaion of the down relay and the energization ofthe up relay determines the up stroke of the shear blade, it thenbecomes apparent that the hold down pilot valve can function also duringthe up stroke of the blade. Therefore, as the blade travels upward onits return stroke, a free flow of liquid from the pressure tank willfind its way to the hold down devices to urge the pistons to return totheir normally extended positions, which will be determined by theclearance necessary for insertion of the work beneath the movable bladein preparation for a shearing operation.

The normally extended position of each hold down piston can beadjustably determined by inserting into each of the lines 213 leadingfrom the upper end of each hold down cylinder, a variable choke 249,which may take the form of an adjustable needle valve. Such valve willfunction to limit the rate of flow of liquid from the pressure tank intoeach hold down device during the re turn stroke of the shear blade, andtherefore the normal extended position of each piston when the bladereaches the upper limit of its return stroke.

In order to dispose of any liquid leaking past the pistons in any of thehold down cylinders, the vent fittings are connected to a commonmanifold 251 which in turn empties to a drain tank 253. Liquidaccumulating in this tank may then be pumped through a line 254, backinto the accumulator or pressure tank by means of a pump 255 which maytake the form of a cylinder 257 mounted on a fixed portion of themachine, and a piston 259 affixed to the ram or movable blade wherebythe piston will move in accordance with movements of the shear blade.

A check valve 261 between the drain tank 253 and the pump 255 precludesreverse flow during the work stroke of the pump and likewise, a checkvalve 263 in the line 254 precludes reverse flow from the pressure tank219 to the pump 255 during such stroke.

A connection 265 from the upper end of the pump cylinder to the line 254permits of liquid flowing in behind the piston during a work stroke andthereby precludes development of a vacuum condition. During the intakestroke of such piston, such liquid will be pumped out of the cylinder,and to assure that it does not enter the suction side of the pumpcylinder, a second check valve 267 is placed in the line 254, betweenthe discharge opening of the pump and the connection 265.

Working in conjunction with the hold down devices is a provision forassuring that the ram will, at all times, function under positivecontact with the Ways on which it rides.

A vertically moving ram will during moments of movement under no loadconditions, tend to swing away from its associated ways, and this isparticularly apt to be the case, when the ways are tilted to a slightangle as heretofore described. Further, under conditions developed whenthe hold down devices engage the work or work support, a small moment iscreated which tends to force the ram away from positive contact with theways.

To counteract such tendencies, a pull back assembly 269 is connectedbetween the ram at each end thereof and a fixed component of themachine, in this instance, the adjacent side wall of the frame. Suchassembly involves a cylinder 271 pivotally secured at one end to theside wall and enclosing a piston 273 having a piston rod 275 extendingthrough the other end of the cylinder for hinge connection to the ram,or more specifically, the stiffening rib. A spring 277 about thatportion of the rod within the cylinder and under compression between theadjacent end of the cylinder and the piston, serves to hold the ramunder light positive pressure against the ways, which pressure isadequate for no load conditions.

To build up such pressure, the cylinder is hydraulically connected by aflow line 279 to the same line that carries the liquid to and from thehold down devices. Thus, as the hold down devices engage the work orwork support, the pressure built up therein by the driving movement ofthe ram, will at the same time be transmitted to the pull backassemblies, and such increased pressure will more than compensate forthe effect of the turning mo ment created by the hold down devicesduring the period in which they function.

As a safety precaution against damage to the machine in the event theram or blade, from some unforseeable cause, be tilted beyond the almostmicroscopic range taken care of by the micro-switches 169 and associatedvalves, there is provided circuit means for cutting power to the machineto bring the same to a halt.

This precautionary measure involves a pair of normally closedmicro-switches 285, 287 disposed on either side of the pivot rod 175 inspaced relationship to the lower end thereof by a distance such as willnecessitate a greater swing of said rod to actuate these switches thanwould be required to actuate the leveling switches 165, 1167. Thesenormally closed switches are in series in a main power lead 288 whichcarries current to the control circuits.

Between this lead and the opposing power lead is connected to thesolenoid 289 of a normally open valve 291, which by reason of the factthat the micro-switches are normally closed, will be energized to itsclosed condition during normal operation of the machine. This valveopens to the tank 47 and has a pilot connection 293 to the relief valve73 which, when open, serves to circumvent the spring setting of suchrelief valve and permit substantially free opening of said valve.

Thus when the valve 291 opens in response to opening of either one ofthe micro-switches 285 or 287, the output of the pump will be dischargeddirectly back to the tank. At the same time, electrical power will bedisconnected from the control circuits.

A normally open push button switch 295 in shunt across the seriesconnected micro-switches will enable an operator to temporarily connectpower to the machine if desired.

From the foregoing description of the invention, it will be apparentthat the same fulfills the objects attributable thereto. While the samehas been illustrated and described in its preferred form and inconsiderable detail, the invention is subject to alteration andmodification without departing from the underlying invention andaccordingly it is not desired that the scope of protection be limited tosuch details except as may be necessitated by the appended claim.

I claim:

A hydraulically operated shear machine comprising a frame; a normallysubstantially level shear blade having a sloping cutting edge wherebythe load on said blade is concentrated on a small longitudinal incrementof said edge and shifts progressively therealong during a shearingstroke of said blade; means included in said frame for supporting saidshear blade for substantially vertical reciprocal movement; a hydraulicsystem for driving said blade, said hydraulic system including a pair ofcylinder assemblies, each mounted on said frame in drive connection withsaid blade adjacent an end thereof and involving a cylinder and a pistonreciprocally disposed therein, the effective area of one of said pistonsexposed to operating fluid pressure during a shearing stroke beinglarger than the corresponding effective area of the other piston; meansfor supplying liquid under pressure from a single source to saidcylinder assemblies in series; and means responsive to a tilt of saidblade from its normally substantially level position solely during aretraction stroke thereof, for restoring said blade during said stroketo its normally substantially level condition, said means including anormally closed solenoid actuable valve in bypassing relationship to oneof said cylinder assemblies as respects the supplying of pressure fluidthereto during a retraction stroke, a normally closed solenoid actuablevalve in bypassing relationship to the other of said cylinder assembliesas respects the supplying of pressure fluid thereto during a retractionstroke, and means actuated by said blade in its tilted position during aretraction stroke for opening the bypass valve of the cylinder assemblyat the advanced end of said blade until said normally substantiallylevel condition is restored and renders said responsive meansinefiective, thereby to avoid the effects of an accumulation ofdepartures from the normal position of said blade.

References Cited in the file of this patent UNITED STATES PATENTS1,616,856 Huston Feb. 8, 1927 2,286,798 Flowers June 16, 1942 2,302,132MacMillin et al. Nov. 17, 1942 2,558,071 Castle et a1 June 26, 19512,616,265 Wilson Nov. 4, 1952 2,781,844 Pearson Feb. 19, 1957 FOREIGNPATENTS 1,137,783 France Ian. 21, 1957

